conntrack: Fix Windows build due to ternary syntax extension.

In the cited commit a ternary using syntax extension slipped in.

The extension allows omitting the second operand and it is not
supported by MSVC resulting in a build failure.

Fix it by simply specifying the second operand.

Fixes: b57c1da ("conntrack: Use a per zone default limit.")
Reported-by: Ilya Maximets <i.maximets@ovn.org>
[Paolo: added commit message]
Co-authored-by: Paolo Valerio <pvalerio@redhat.com>
Signed-off-by: Paolo Valerio <pvalerio@redhat.com>
Signed-off-by: Aaron Conole <aconole@redhat.com>
Signed-off-by: Eelco Chaudron <echaudro@redhat.com>

lib/conntrack.c

@@ -313,7 +313,7 @@ zone_limit_get_limit(struct conntrack *ct, struct conntrack_zone_limit *czl)
 
     if (limit == ZONE_LIMIT_CONN_DEFAULT) {
         atomic_read_relaxed(&ct->default_zone_limit, &limit);
-        limit = limit ? : -1;
+        limit = limit ? limit : -1;
     }
 
     return limit;